How should an expression matrix look?

Question

[María Montero]

Hello everybody.

I am new to doing data analysis. So I have this problem.

I have to download mRNA and miRNA data from TCGABiolinks, this is one of my two queries.

and then I'm supposed to apply some functions to discretize it and calculate the Mutual Information.

As you can see, this function requires an expression matrix. My question is: how should it look? I mean, after download RNAm and miRNA data can I just save the matrix without filter anything from it and then put it in the function? or should I filter specific values?

Thank you so much and I'm sorry if I don't know how to portrait my doubts, I'm a bit lost.